Electron discharge system



y 1932- M. A. ACHESON I ELECTRQN DISCHARGE SYSTEM Filed March 28. 1930Fig. I.

Pig. 2.

ELECTROMOTIVE FORCE APPLIED BETWEEN GRID AND CATHODE Pig. 4.

Fig. 3.

Inventor- Marcus A. Acheson,

His Attorney.

Patented May 10, 1932 UNITED stares rarnnrorrice MARCUS A. .AOHESONOFSCHENECTADY, NEW YORK, ASSIGNORTO' GENERAL ELECTRIC 7 COMPANY, ACORPORATION; OF NEW YORK ELECTRON DISCHARGE SYSTEM Application filedMarch 28, 1930. Serial No. 439,792.

My invention relates to systems employing electron discharge devices,and it has among its objects to provide a method and means foreliminatingundesired effects in the circuits of electron dischargedevices caused by emission of secondary electrons from the grid to theanode.

More; particularly it has for its purpose to provide means forpreventing the produc- 10 tion of undesired oscillations in the circuitsassociated withflthe grid and cathode due'to negative resistance in thegrid circuit of the discharge deviceresulting from the emission ofsecondary electrons from the grid.

Another object of the invention is to provide means in the circuitwhereby the resistance of the circuit looking toward the dischargedevice from those portions, of the circuits which are capable ofoscillating at undesired frequencies, is positive, constant,

or insufliciently' negative tosupport oscillationsin the circuit. Inaccordance with the invention this resistance may be varied as desiredover a considerable portion ofthe range of grid voltage variations overwhich negative resistance within the discharge device occurs.

. The novel features which I believe to be characteristic of myinvention are set forth with particularity in the appended claims. Myinvention itself, however, both as to its organization and method ofopera:tion,together with further objects and advantages thereof, maybest be understood by reference \3 to the following description taken inconnection. with the accompanying drawings in which Fig. I represents anelectron discharge circuit arrangement employing my invention; Fig. 2represents certain of the. characteristics thereof, and Figs. 3. and 4represent modifications of my invention as shown in Fig. 1.

Referring to Fig. 1 of the drawings I have shown a conventional electrondischarge amplifier circuit in which oscillations to be amplified aresupplied from a source. 1' through an input transformer 2130 the grid ofan electron discharge device 3. Both the grid and the anode circuits ofthe discharge device 3 are tuned to the operating'f'requency asindicated by the tuned circuits 4 and 5. I A load ated'at positivepotential with respect to the cathode during a portion of the cycle ofoscilla-tions to be amplified that bombardment of the grid withelectrons from the cathode causes an emission of secondary electronsfrom thegrid, these secondary electrons being attracted away by the morepositive anode. The number of secondary electrons emitted from the gridis dependent upon the velocity with which primary electrons hit thegrid, which in turn is dependent upon the voltage applied between thegrid and cathode. As the grid potential increases in a positivedirection over a certain range thereof,

the number of electrons emitted from the grid increases and may becomeequal or greater than the number of primary electrons which hit thegrid, thereby imparting to the space between the grid and cathodeanegative resistance characteristic over a portion ofthe range of gridvoltage variation,

This characteristic of the discharge device is indicated by the curve 9in Fig. 2. This curve represents the relation between the currentflowing in the grid circuit and the electromotive force applied betweenthe grid and cathode. It will be seen that as the grid voltage isincreased from zero the grid current likewise increases to a pointindicated at A on the curve. At this point the velocity of electronsbetween the cathode and grid be comes sufliciently great to cause acertain number of secondary electrons to be driven off from the grid dueto bombardment of the grid by the primary electrons from the oathode.These electrons are attracted away from the grid by the niore'positiveanode and represent a flow of current in the grid circuit opposite indirection to that represented by the primary electrons. Thus, the totalcurrent flowing in the grid circuit then starts to decrease and as thegrid becomes more positive the emission of secondary electrons continuesto increase until their number is equal to the number of primaryelectrons which reach the grid, at which time the current in the gridcircuit is zero, as indicated by the point B on the curve 9. As the gridbecomes still more positive the number of secondary electrons stillincrease until a point is reached, as represented by the point C, atwhich the anode is insufliciently positive to attract all of thesecondary electrons which are emitted from the grid. These electronswhich are not attracted to the anode thus fall back into the grid. Thusfrom this point on as the grid potential is increased the current in thegrid circuit continues to increase, as shown by the portion of the curve9 at the right of the point C.

It will be seen that over that portion of the range'of grid voltagevariation between the points indicated at A and G on the curve 9 thereis a decrease in current as the grid voltage increases or, in otherwords, the space between the grid and cathode has negative resistance.

Due to this negative resistance, as is well known in the art,oscillations are likely to be set up in the circuits which areassociated with the grid. These oscillations may appear in any portionof the circuit which is capable of resonance at a parasitic frequency asin the leads extending to the grid bias voltage of a practicalinstallation, or in the tuned circuit 4, or elsewhere in the circuit.Among other undesirable effects which are likely to be produced byoscillations of this kind is that of parasitic modulation of theoscillations amplified by the device 3.

In accordance with the present invention the undesired effects of thenegative resistance of the discharge device are obviated by connectingacross the grid circuit a path indi cated at 10 in Fig. 1 havingpositive resis ance. This path, as shown in the figure, comprises aresistance 11 and an electron discharge device 12. V The dischargedevice 12 is of any suitable two-element type having its anode connectedthrough the resistance 11 to the grid of the discharge device 3, and itscathode connected to the cathode of the discharge device 3. The currentflowing in the path 10 varies directly as the electromotive forceapplied to the grid of the discharge device 3. This current may berepresented by the curve 13 of Fig. 2. The total current flowing in thegrid circuit of the discharge device is then the sum of the currentsflowing 1n the path 10 and that flowing from the grid of the dischargedevice 3. In other words, it is the sum of the currents represented bycurves 9 and 13 of Fig. 2. This total current is indicated by the curve14 of Fig. 2.

It will be seen that this curve represents a positive resistancethroughout the entire length thereof; that is, the resistance of the twoparallel paths comprising the path 10 and the path between the grid andcathode of the discharge device 3 is positive throughout the entirerange of voltage variations.

The path 10 may be connected across the grid circuit at a pointsufliciently close to the discharge device 3 to preclude the possibilityof the currents of parasitic frequencies being set up in the conductorextending from the grid of the discharge device 3 to the branch circuit10. Since the resistance of the circuit, as measured at all points tothe leftof the branch 10, is positive, the effect of negative resistancein the discharge device 3 is obviated.

Due to the damping of the grid circuit, however, it is unnecessary toentirely obviate the negative resistance so long as it is maintained ata value which is insufficiently negative to overcome the damping effectof the circuit, and thus cause'oscillations to be produced. Thus, ifdesired, the slope of the curve represented at 13 of Fig. 2 may bevaried by varying the resistance 11 included in the branch circuit. Inthis way the slope of the curve 1 1- over that range-of variations in'grid electromotive force in which negative resistance is likely tooccur, may be varied, and, if desired, may be caused to represent anegative resistance within a range, as in dicated above, whiohmay betolerated. If desired this resistance may be made substantially constantover a considerable portion of the range in which negative resistance indevice 3 occurs.

A .considerable economy in the energy expended in the grid circuit,however, may be efi'ected by biasing the anode of the discharge device12 negatively with respect to the oathode. This modificationot theinvention is shown in Fig. 3 in which a source of electromotive force 15is connected in the branch circuit 10 and so polarized that the anode ofthe discharge device 12 is negative with respect to the cathode. As thusarranged, it is necessary that a greater positive potential be appliedto the grid of the discharge device 3 before current starts to flow inthe branch circuit 10. The source of potential 15 may be so adjustedthat the flow of current in the branch circuit 10 begins approximatelyat the same value of grid electromotive-force at which the emission ofsecondary electrons begins, thiscurrent increasing with respect to gridvoltage represented by the curve 16 of Fig. 2. The total current flowingin the grid circuit may then be represented by the curve 17. This curverepresents a very considerable reduction in the amount of currentflowing in the grid circuit, and, at the same i be varied as before byvariation of resistance 11 thereby to control the slope of the curve 17over Whichnegative resistance is likely to occur.

InFig. 4 I have represented a further modification of the invention inwhich the source of biasing potential 15 isreplaced by a resistance 18shunted by a condenser 19. The

condenser 19, after the first few cycles of applied electromotive forceof the source 1 t0 the grid of discharge device 3 assumes a-fairlydefinite charge causing the anode of the discharge device 12 to becomenegative with respect to the cathode. This charge may, of course, bevaried by varying the resistance 18 and, hence, by varying theresistance 18 the value of grid electromotive force at which currentstarts to flow in the branch circuit 10 may be varied. Thus curve 16maybe shifted, either to the right or to the left, by vari ation of theresistance 18. The slope of the curve 1-6 may of course be varied byvarying the resistance 11.

The use of the asymmetrically conducting discharge device 12 in the path10 is particularly advantageous not only in that the point at which theflow of current begins may be readily adjusted but also in that itprevents the flow of current therethrough and the consequent waste ofenergy in the grid circuit during the portion of the alternating currentcycle when the anode is negative as would be the case were the path 12conducting in both directions. Further the resistance of this deviceemployed as described may be sufiiciently high to prevent objectionabledistortion of the oscillations supplied to the grid due to energyshunted through the asymmetrically conducting discharge device.

While I have shown in the drawings a conventional amplifier circuitemploying a threeelement electron discharge device, it will of course,be understood that I contemplate the use of my invention in connectionwith discharge devices having any greater number of electrodes in whichany of the electrodes is sufiiciently positive to produce a negativeresistance between the grid and cathode, and, in fact, in connectionwith multi-electrode discharge devices generally.

While I have shown particular embodiments of my invention, it will ofcourse be understood that I do not wish to be limited thereto since manymodifications, both in the circuit arrangement and in theinstrumentalities employed, may he made, and I contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

hat I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. The method of operating a three-elem'ent electron discharge: devicehaving a, grid and cathode,and; conductors'connected thereto, saidconductors being connectedin circuit relation, and in whichsufiicientemission of secondary electrons from the grid may occur to produce anegative resistance be tween the gridandcathode which, includes causingsufficient unidirectional current varying directly as the voltagebetween said conductors to flow from the, cathode conductor to the gridconductor and through said external circuit to cause the current ,in theexternalcircuit to remain approximately constant over a5range ofvoltagevariations between said conductors.

2;. In combination, an electron discharge device having a grid, acathodeand a third electrode, a circuit connected between the grid and cathodeincluding a source of variable electromotive force, a source ofelectromotive force connected between the third electrode and cathode,the relative values of said eleetrom-otive forces being such that thecurve representing the relation between the current flowing in the gridcircuit and the electromotive torce between the grid and cathode has anegative slopeover a portion of the range of variations of gridelectromotive force, and means for causing addi tional unidirectionalcurrent to flow in the circuit connected to the gridand cathode, saidmeans being such that the curve expressing the relationv between theelectromotive force of said grid and said additional currenthas a slopesubstantially equal and opposite to the negative slope of saidfirstmentioned curve over the range of variations of grid electromotiveforce.

The combination,rin an electron discharge amplifier having an 'anode,acathode and, a grid, of an input circuit including a source ofoscillations-to be amplified connected between the grid and cathode, anoutput circuit for amplified oscillations connected to the anode andcathode, means for impressing a positive. potential onsaid anode, theamplitude of saido scillations to be amplified and said anode potentialbeing in relation to. cause a negative resistance between the grid andcathode over a portion of the cycle of said oscillations, and means toovercome theefiect of said negative resistance produced during saidemission of secondary electrons, comprising an electron discharge devicehaving an anode connected to said grid and a cathode connected to thecathode of said' amplifien.

l. The combination, in an electron discharge amplifier having an anode,a cathode, and a grid, of an input circuit including a source'ofoscillations to be amplified connected between the grid and cathode, anoutput circuit for amplified oscillations connected to the anode andcathode, meansfor impressthe same portion of ing a positive potential onsaid anode, the amplitude of said oscillations to be amplified and saidanode potential being in relation to causea negative resistance betweenthe grid and cathode over a portion of the cycle of said oscillations tobe amplified, a conducting path between the grid and cathode includingan electron discharge device and a source of potential, the potential ofsaid source having such a value that substantially no current flows insaid path except during those portions of the cycle of said oscillationswhen the potential on the grid is sufficiently positive to cause thegrid to have negative resistance.

5. In combination, an electron discharge amplifier, having a grid andcathode, a circuit conductive to direct currents and including a sourceof oscillations connected to the grid and cathode whereby the grid iscaused to become alternately positive and negative with respect to thecathode, and a path connected across said circuit including anasymmetrically conducting discharge device and a source of biasingelectromotive force, said electromotive force being such that currentflows in said discharge device only during that portion of alternatehalf cycles of said oscillations when the potential on the grid issufficiently positive to cause the grid to have negative resistance.

6. The combination, in an electron discharge amplifier having an anode,a cathode and a grid, of an input circuit including a source ofoscillations to be amplified connected between the grid and cathode, anout put circuit for amplified oscillations connected to the anode andcathode, means for impressing a positive potential on said anode, theamplitude of said oscillations to be ainplifie-d and said anodepotential being so related as to cause a negative resistance between thegrid and cathode over a portion of the cycle of said oscillations, apath having positive resistance connected across said circuit, said pathbeing conductive only during that portion of the cycle of saidoscillations when the'grid is sufiiciently positive with respect to thecathode to cause the emission of secondary electrons therefrom, andmeans for varying the value of grid electromotive force at which saidpath becomes conducting.

7. In combination, an electron discharge device having an anode, acathode and a grid, a circuit between the grid and cathode including asource of oscillations to be amplified, a circuit for the amplifiedoscillations connected between the anode and cathode, means forimpressing a positive potential on the anode of such value with respectto the amplitude of said oscillations that negative resistance isproduced between the grid and cathode during a portion of the positivehalt cycle of said oscillations, an asymmetrically conducting dischargedevice having a cathode connected to said first mentioned cathode and ananode connected to said grid, the combined resistance of saidasymmetrically conducting discharge device and the negative resistancebetween said grid and cathode being insufficiently negative during saidportions of the positive half cycle of said oscillations to be amplifiedwhen said negative resistance is produced to cause the production ofundesired oscillations in the grid circuit.

8. In combination, an electron discharge device having an anode, acathode and a grid,

a circuit between the grid and cathode including a source ofoscillations to be amplified, a path between said grid and cathodeincluding a discharge device conducting only when the grid is positive,means for impressing a positive potential on the anode the amplitude ofsaid oscillations being sufficiently great to cause a negativeresistance between the grid and cathode duringca portion of the positivehalf cycle of said oscillations and the combined resistance of said pathand said negative resistance being insufiiciently nega tive during saidportion of the positive half cycle to prevent the production ofundesired oscillations in the grid circuit and the resistance of saidpath being sutficiently high substantially to prevent distortion of thepositive half cycle of said oscillations due to energy shunted throughsaid path.

9. In combination, an electron discharge device having an anode, acathode and a grid, a circuit between the grid and cathode including asource of oscillations to be amplified, a circuit for the amplifiedoscillations connected between the anode and cathode, means forimpressing a positive potential on the anode of such value with respectto the amplitude of said oscillations that negative resistance isproduced between the grid and cathode during a portion of the positivehalf cycle of said oscillations, an asymmetrically conducting dischargedevice having a cathode connected to said first mentioned cathode and ananode connected to said grid, a source of electrornotive force includedin circuit with said asymmetrically conducting discharge device of sucha value that current flows in said discharge device only when thepotential on said grid is suificiently positive to cause said negativeresistance to occur between said grid and cathode, and a resistance inseries with said asymmetrically conducting discharge device of such avalue that thetotal change in current in said circuit between said gridand cathode is small with respect to the change in grid voltage overthat portion of the half cycle where said negative resistance occurs.

10.'In combination, an electron discharge device having an anode, acathode and a grid, a circuit between the grid and cathode including asource of oscillations to be amplified, a circuit for the amplifiedoscillations connected between the anode and cathode, means forimpressing a positive potential on the anode of such value with respectto the amplitude of said oscillations that negative resistance isproduced between the grid and cathode during a portion of the positivehalf cycle 01" said oscillations, an asymmetrically conducting dischargedevice having a cathode connected to said first mentioned cathode and ananode connected to said grid, means connected in circuit with saidasymmetrically conducting discharge device for producing from thecurrent flowing through said asymmetrically conducting discharge devicea continuous unidirectional electromotive force of such value as toprevent the flow of current through said asymmetrically conductingdischarge device except when said grid is sufiiciently positive withrespect to the cathode of said first mentioned discharge device toproduce said negative resistance.

11. In combination, an electron discharge device having an anode, acathode and a grid, a circuit between the grid and cathode in cluding asource of oscillations to be amplified, a circuit for the amplifiedoscillations connected between the anode and cathode, means forimpressing a positive potential on said anode of such value with respectto the amplitude of said oscillations to be amplified that a negativeresistance is produced between the grid and cathode during a portion ofthe positive half cycle of said oscillations, an asymmetricallyconducting discharge device and resistance connected in series betweensaid grid and cathode, anda condenser connected in shunt with saidresistance whereby an electromotive force is maintained on saidresistance of such magnitude as to prevent the flow of current throughsaid discharge device until said grid is sufliciently positive withrespect to the cathode to cause said negative resistance between thegrid and cathode.

In witness whereof, I have hereunto set my hand this 27th day of March,1930.

MARCUS A. AOI-IESON.

